A typical excavator housing positioning system includes a hydraulic motor that rotates gears associated with a swing gear train, which in turn, rotates the housing. A closed loop control system may be used to position the excavator housing to a desired position.
Conventional closed loop control systems directly measure the parameter to be controlled. In this case, the control system directly measures the rotational position of the excavator housing, compares the measured position to a desired position and calculates an appropriate motor command to minimize the difference between the two positions. However, the manufacturing tolerances associated with the swing gear train lead to an amount of freeplay or backlash between the swing gear train and the housing. The freeplay causes the excavator housing to "drift." Because the control system attempts to control the excavator housing to the desired position, the "drifting" motion causes the control system to become unstable. The instability of the control system produces undesirable oscillations of the excavator housing.
The present invention is directed to overcoming one or more of the problems as set forth above.